David -
I have also been experiencing this oddball aim issue when attempting to insert clipboard contents into a specific point in Mail. I am writing to lend credence to the contention that this is an Apple Mail issue that really should be fixed. Apple started the cut & paste revolution and the fact that one of their key software packages cannot paste properly strikes me as a bit ludicrous.
This started happening on both my iMac and MacBook Pro a few months ago. It could be that it correlates with my use of three different styled signature files for three different e-mail accounts (I hadn't thought of the connection, so thank you, I had been wondering if they had altered something in one of their many security updates).
I desired that the body text of my e-mail default to something different from the style of my signature files. Mail is fairly limited in this area, so I include a top line my signature file that has the right style for my body text. Now I start all messages by overwriting that styled text, so my message font is as I want it. Is this the source of the problem?
The inability to place text correctly isn't restricted to pasting something in via clicking on a particular spot in the e-mail. Odd things also happen if you use the directional arrow keys to move the cursor around with the keyboard and then command-V, or if you drag text to a certain spot, and when you release, it refuses to go there.
There's some logic to the mistakes. The text is almost always placed a couple of lines above where the insertion point is blinking, and you can fool Mail sometimes by placing text in the middle of a bunch of new returns and then deleting the surrounding lines, but this is cumbersome and annoying.
I hope Apple reads this, because it got so annoying that I switched to Outlook (Office 11) and it's terrific in some of the areas where Mail falters (work e-mail is Exchange). About the only thing that Mail does better is access my MobileMe folders much more quickly.
Come on, Apple!